We have noticed that you have customized the Dokan plugin. This is the file where you have edit the code plugins/dokan/templates/update-account.php. That is why the several “become a seller” button are generating in the account migration page. We alredy fixed this error. Can you please check.
Can you please remove and backup the old Dokan plugin. Also download again the Dokan latest plugin and put in the plugin folder. If there were have any customization then it will be erased and replace with the new plugin.
I have tried to reproduce this issue but failed. It could be a has a chance of theme or plugin conflicts. You can disable all your plugins except Dokan and switch to a default theme of WordPress like – Twenty Twelve, Twenty Thirteen, Twenty Fourteen and let me know the results.