If I was you I?d:

1. Wash the area with soapy water to remove the previous residue.
2. Optional: A final wipe with isopropyl alcohol.
3. Use painters tape or masking tape to mark out and border the areas you wish to paint. You can try freehand if you got a steady hand but even I couldn?t do it.
4. Apply a white primer to the area you wish to paint. Tamiya (https://www.tamiya.com/english/produ...ace/index.html) Vallejo and Mig Ammo are all good brands.
5. Once primer has dried apply the yellow paint. Again, I recommend acrylic or enamel paint.
6. Once yellow paint has dried, remove the tape.
7. If you can be bothered you can apply a clear top coat to seal the paint but its extra cost for such a small area. The primer is the most important step.