I put a fan on in coil section and freezer works great.
Which coil section?
There are two in the unit.
The condenser coils are under the unit close to the compressor.
The evaporator coils are inside the freezer.

Both theses sections already have their own fans.
Are these fans running?

Sounds like an air flow/condenser coil cooling problem.
I am assuming that this unit used to work OK for you and that it is not new to you.

Check that all vents a clean.
Check that the condenser fan blades are clean. Dust ones can greatly reduce air flow.
Check/clean the condenser coils.
Remove power from it and spin the condenser fan blades to see if it is OK.

When it gets too warm does the compressor run continuously?
if yes.
There is a possibility that the unit has a sealed system problem and you are just on the edge of maintaining freezer temperatures.
I would check the freezer temperature it should be between 0 and 5 degrees F.
If higher then I would remove the cover in the freezer so i could inspect the evaporator coils.
They should have a fairly even layer of frost across them.
f there is just frost in one area then you may be low on freon.
Be sure that the unit has run for at least an hour because if you do this shortly after or during a defrost cycle you may come up with the wrong diagnosis.