My jeep wrangler 1991 its blowing some oil into the air filter, how can I fix this?

First thing you need to do is check the venting system. Jeeps use either a PCV valve or a ported valve.
In either case, make sure that the valve on the valve cover is clean and able to flow. PCV valves are not expensive so I'd just replace it if you have one, CCV (ported) can be cleaned out with a small wire and carb cleaner.
Make sure that there is vacuum present at the valve, if not, clear the line or fitting of carbon.
Both systems can only function well if the engine itself is in good condition. If you have worn piston rings, crank case pressure rises above the capacity of the system and excess pressure will vent to the air filter.
If that is the cause, nothing short of rebuilding the engine will stop it from doing that but I have seen some that people have removed the hose from the air filter box and diverted it into a vented "catch can"
so it doesn't foul the filter. it's not a "fix" but keeps the oil off the filter.

This is the classic signs of excessive piston blowby and a build-up of compression in the crank case. The only solution, unfortunately, is a complete sub assembly overhaul. Just to confirm the above, try taking the dip stick out while the engine is running, but stand clear, you could collect a spray of oil.