You can directly type the query commands into the Instant Search box to search with multiple keywords in Outlook. Please do as follows:

subject:"keyword 1" And subject:"keyword 2" And subject:"keyword 3" And …
In the Mail view, type the query command of subject:"test" And subject:"change" into the Instant Search box, and then specify the search scope in the Scope group on the Search tab.
And now all emails whose subjects contains both keywords of test and change are found out and listed in the mail list. See screenshot:

subject:"keyword 1" OR subject:"keyword 2" OR subject:"keyword 3" OR …
In the Mail view, type the query command of subject:"test" OR subject:"change" into the Instant Search box, and then specify the search scope in the Scope group on the Search tab.
And now all emails whose subjects contain any keyword of test or change are found out and listed in the mail list. See screenshot:

Note: the logic words of And and OR in the criteria should be uppercase.

One click to enable Query Builder and easily search with multiple keywords in Outlook

Kutools for Outlook can help you enable the Query Builder in Advanced Find dialog box with only one click. Within the Query Builder tab, you can add multiple search keywords, and specify the logical relationship "AND" or "OR" amount these keywords. 

To search emails whose subjects contains any keywords of test or change, you can also apply the Advanced Find feature in Outlook. Please do as follows:

1. Press Ctrl + Shift + F keys together to open the Advanced Find dialog box, and go to the Advanced tab.

2. Click the Browse button to specify the search scope as you need.
Note: You can specify multiple folders in the same email account as search scope. However, it does not support to search multiple folders in different email accounts.

3. In the Advanced tab, specify the search criteria as follows: (1) Select Filed > All Mail fields > Subject; (2) select contains from the Condition drop down list; (3) type the first keyword into the value box; and (4) click the Add to List button. See screenshot above.

4. Repeat above Step 3 to add search criteria with other keywords one by one.

5. Click the Find Now button.

And now all emails whose subjects contain any keywords of test or change are found out from the specified search scope and listed at the bottom of the Advanced Find dialog box

For searching emails containing any one keyword of test or change in subjects, or all emails containing both keywords of test and change in subjects, I recommend you to enable the Query Builder tab with Kutools for Outlook, and then specify the search criteria as you need.

1. Enable the Query Builder tab in the Advanced Find dialog box as follows: (1) click Kutools > Options, (2) in Options dialog box, check the Restore “Query Builder” tab in Outlook Advanced Find Dialog option on the Others tab, and click the OK button. See screenshot:

2. Press Ctrl + Shift + F keys to open the Advanced Find dialog box, and do as following screenshot shown:

(1) Click the Query Builder tab;
(2) Click the Browse button to specify the search scope as you need;
(3) Specify search criteria as Subject contains test and Subject contains change
(4) Select Or or And as you need from the Logical Group drop down list;
(5) Click the Find Now button.

And now all emails whose subject contain any keyword of test or change are found out from the specified search scope, and listed at the bottom of Advanced Find dialog box.

Search with escape/special characters in Outlook

Print search results in Outlook

Make case-sensitive search in Outlook

Search (partial word) with wildcard in Outlook