I entered into a MOU to sell my apartment and the buyer changed his mind. How to claim deposit?

I entered into an MOU to sell my apartment but unfortunately, my agent didn’t collect the security cheque from the buyer’s agent at the time of signing the MOU.

Two days later, the buyer changed his mind and wanted to cancel the deal.

Now in this situation:

How can I claim the security deposit amount from the buyer?

Will it involve any legal process?

If yes, then how long does it take and how much does this cost?

Should I just cancel the deal with the buyer and move on with selling my apartment to another buyer?