If you want to repair your car in Bitlife, you will to first find your car under assets and click on it. After this, you can repair your car via an option called repair, and using it will increase and improve the condition of your car.
Another option is similar to this is called maintenance, and it performs a similar role; however, instead of you doing repairs, it's someone else. That said, if you want to use the maintenance option, you will need to visit the same tab where you found the repair one.
Related: How to buy and sell a car in Bitlife
Under your car's asset tab, you can find it labeled and maintenance, and using it will schedule your car for routine maintenance. Once scheduled, it should increase the condition of your car after you age by one year. We also only recommend using this option if you have money to spare as it will cost a small each time you use it.
You will also need to do this a few times to complete one of the objectives in this week's challenge, along with repairing the car. However, before you can even use any of these options, you will first need to get a car. If you don't know how you can buy one from a car dealer via an option under the go shopping tab.
For more on Bitlife, check out How to Become a Mechanic in Bitlife and How to complete the Motorhead Challenge in Bitlife