Something like

semanage fcontext -a -t mysqld_db_t "/yourdirectory(/.*)?"

then

restorecon -Rv /yourdirectory

??

To set mysql selinux on a directory you can:

semanage fcontext -a -t mysqld_db_t "/yourdirectory(/.*)?"

then

restorecon -Rv /yourdirectory

Also check the mysql user has permissions on your directory:

ls -l

Set permissions if needed:

chown -R mysql:mysql /yourdirectory