To install MySQL 5.7, you should enable MySQL 5.7 community release yum repository on your system.
STEP 1. Enable MySQL Repository
yum localinstall https://dev.mysql.com/get/mysql57-community-release-el7-9.noarch.rpm
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
Change password by the pre-defined password above
mysqladmin -u root -p password
STEP 5. Initial MySQL Configuration
/usr/bin/mysql_secure_installation
Note you can use the temporary password acquired at STEP 4.