The verb forms of fix are fix, fixed, fixes, fixing.
Fix is an irregular verb, its present simple and past simple form are both “fix”. The present continuous form of “fix” is “fixing” and the past participle form is “fixed”. For example, you can use “fix” in a sentence like this - “I fixed the lock on the door”.
You can also use the verb “fixes” - “He fixes things all the time”.
So as you can see, there are four forms of the verb “fix” - fix, fixed, fixes, and fixing.