Welcome to the forum.
The template asked about is not something you will probably find or need.
Fit the tuners to the neck and snug them up but not too tight with the washers and nuts from the front of the headstock. You then use a small straightedge or set square to ensure they are all aligned.
Once you are happy with the alignment, mark where the screw holes need to go with an awl or similar.
Remove the tuners, drill the pilot holes.
Put the tuners back on, with washers and nuts, not too tight, wax your screw threads and screw them in. Then tighten the nuts at the front to final tightness.
This should go without saying, but make sure you do drill pilot holes, and you do wax the threads of the screws.
As you have not mentioned which specific Grover tuners you will be using the above is a generic set of steps for most tuners.