Are you using phpMyAdmin interface? Does it take longer than 100 seconds to upload and execute the request?
If so, can you try uploading a compressed database or xml file, or even via command line?
The PHP request could continue in the background even if you got 524 timeout error.
I am afraid you cannot change it. You need to finish everything in under 100 seconds. Otherwise you need to change your approach. I believe only Enterprise plans can extend this time.
Other way is to simply and temporarly unproxy your DNS record by switching to 
as the documentation from below suggests. Keep in mind, this will reveal your origin’s address (should that be of concern). When finished, switch back to 
cloud.
Suggestions regarding 524 error: