This is not too difficult. I have three 1990 Reattas so have done this a couple of times. Look in the Owners Manual to get the correct bulb, the dealer may or may not have it but auto supply places such as Auto Zone do, it cost about $10, it is not just a bulb, it is a small module with the bulb in it. Repalcing this bulb is almost like changing the oil. You'll have to crawl under the front bumper and remove 2 screws from the 3-inch splash guard so you can get the splash guard out of the way, you do not have to remove the entire splash guard. Then just reach up to the turn-signal bulb module and pull it out, it may take a little wiggling to get it out if it has been there for a number of years. Then put in the new module. Once you buy the replacement module and look at it, it becomes obvious what to do and which of the many lights is the turn-signal. The smaller the fingers, the easier it is to do as it is a tight fit. If you have a big hand with larger fingers, it may be more difficult. It took me 30+ minutes the first time I did it as I had to figure out what to do, but the last time ( 6 months ago) it took about 10 minutes.
Open the trunk lid and pull the upholstery from the rear of the trunk. You will find white and black plastic wing nuts. Remove the white ones on the side you are working on and swing the lens assembly up. If you don't like standing on your head to work on the lights, remove all of the white and black wing nuts and pull the tail light assembly to the rear. Replace the bulbs. Jack
Top of the motor where a big black hose attaches ull cc sum bolts look like the hold hose on that's it.
You don't. You replace it. They're cheap. Get a new one. No matter how much you clean it, it will never work right.