If you are having the redirection loop problem while trying to access wp-admin then try this fix.
change the permission of wp-admin/index.php to 755.
If you have cpanel access then browse to file manager then browse to wp-admin. Then right click on index.php and then change permission and then uncheck Write checkbox
Right click index.php
Change permission as shown in image below.
Save the changes, you have made and retry to access the wp-admin.
If this doesn’t work for you then you have to look for error_log file in the root of your public_html that should point you to the correct direction in solving this issue.