Sitting down cows upright that are bloated can fix the problem.

Truely mild bloated cows can be treated with drenching around 100ml of bloat oil or vegetable oil.

As a last resort stab the cow. LEFT HAND SIDE ONLY  At the highest point which is just behind the ribs and a hand down from the backbone.

Use a knife with hand protection and only open about 5cm

Of grass blocks the gas remove it by hand or push a bit of 1.5 inch pipe into the rumen.

Treat with 12ml meloxicam or similar in vein or under skin. Consult vet.