You have two options here.
One is that the brake is locked on at the wheel and needs to be loosened. Check where it is and try to make sure it is loose.
The other option is that since you pushed it with the lever in the wrong place, you may have ruined the hydtro on that side.
This is not the answer that you are really looking for, but is the only answer that makes sense.
Find the best dealer that you can and take the mower to him and say let me know what the problem is and an estimate.
This is not something that a normal person should try to fix. You could cost yourself hundreds of dollors in repairs if you mess something up.
Sometimes the correct answer is not the answer we want to hear.
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