How do you write the following sentence with a defective verb in the past tense?: I can try to fix it.
The correct forms are: I could try to fix it. or I was able to try to fix it.
Although the verb can is defective, it still has a valid Past Simple form "could" so it is possible to use, but it also has a synonyme "to be able to" which can be used in any tense.
These are correct forms:
I was able to try to fix it. - Past Simple
I have been able to try to fix it. - Present Perfect
I will be able to try to fix it. Future Simple