Hello. You must add it to the end of the amount you will send.
For example, you will withdraw 10 Grin and the Memo number is 1598438.
Then you will withdraw= 10.1598438
This is a slightly outdated method, but unfortunately that’s how Gate works.
Note: After the transfer, you will see your Grins on the Gate after an average of 17 hours. 1000 blocks required