Mysql 8 failed install and revert to mariadb 5 6 10

I was trying to remove mariadb to install ver 5,7 or 8 of mysql. I thought i would be able to do mysql 8 as there is a repo availbl https://repo.mysql.com/mysql80-community-release-el7-1.noarch.rpm

i thought mariadb had uninstalled but after yum erase mariadb* and yum remove mariadb* but it stills fails to uninstall. I had initially apparently installed mysql 8 but it never started. So i cleaned /var/lib/mysql and /etc/my.cnf and tried several times to yum remove and then from webmin uninstall manually. After many attempts of mysql 8 not starting I uninstalled it and repo removed> This enabled me to reinstall default mysql mariadb 5.5.10

Is there any way i can remove mariadb successfully without leaving any trace and then try install mysql 5.6 or 5.7 as the older server had mysql 5.6

Can you tell me where is the repo of mariadb? How can i successfully remove it and then re install any KNOWN repo/mysql version?

I shall be grateful for any help.