To install MySQL 5.7, you should


STEP 1. Enable MySQL Repository


STEP 2. Install MySQL 5.7 Server
yum install mysql-community-server

STEP 3. Start MySQL Service
service mysqld start

STEP 4. Checking temporary password
grep 'A temporary password' /var/log/mysqld.log | tail -1
Then you will be able to see its result like below:
2020-04-20T01:50:07.931468Z 1 [Note] A temporary password is generated for root@localhost: #l+wu>PMv7vJ


STEP 5. Initial MySQL Configuration
/usr/bin/mysql_secure_installation
Note you can use the temporary password acquired at STEP 4.