How do I reset Practice Mode quickly?

Click both sticks: L3 + R3 on PS5, LS + RS on Xbox.

Can I start on the ground or in the clinch?

Yes. Practice settings have initial ground position and initial clinch position. Use them.

Only while you learn a new window. Turn it off and repeat at full speed before you queue.

The gym is not for beating a dummy. It is for one skill, ten minutes, then the same skill at full speed.

How to use UFC 6 Practice Mode: set the starting position, turn on time dilation, and drill one skill at a time.