How to deal with the bubbles during the mixing process?

It depends on your practical situation.

Firstly you can deal the mixture with a vacuum machine if you have one;

If no such machine, you can reduce the mixing ratio of the hardener from 4% to 1%-2%.Then in the prior period of the reaction of the mixture will be slower, then the air in the mixture will exhaust by itself for a longer curing time to release the bubble.