Hi, anonymous userPrashant-7984 Welcome to Microsoft Q&A, Thanks for posting your question.
As we understand the ask here is you are facing an issue while restoring the backup on Flexi Mysql Server 5.7.
In this case, you will need to create a mysqldmp schema file and substitute TYPE=MyISAM to TYPE=InnoDB in the .sql to create a table and execute it on the destination flexible server and follow it with data migration.
MyISAM engine is not supported in Azure Database for MySQL, Limitations - Azure Database for MySQL - Flexible Server | Microsoft Learn
Regards
Geetha