As the message says Amazon requires CIDR Address in the security group, not an address range. CIDR is a way to describe network blocks by slicing the 32 bits of IPv4 address into a network part and host part.
The CIDR format is
IP.AD.DR.ES/PREFIX where the PREFIX is the length of the network part of the address in bits. For example network range: 10.0.0.0 - 10.0.0.255 has the first 3 bytes assigned to the network and the last byte used by the hosts in the network. Hence the prefix is 3*8=24 and the network range 10.0.0.0 - 10.0.0.255 is equivalent to CIDR range 10.0.0.0/24.
If your ISP address range is 22.214.171.124 - 126.96.36.199 it means that the first 12 bits of the address is their networkblock and the last 20 bits they can assign to hosts or internal networks. Hence the answer to your question is 188.8.131.52/12 - use this in the Security Group.
To calculate CIDRs from address ranges you can use for example https://ip2cidr.com/ or many other online tools.
I won't go into more details about CIDR here, read it up on Wikipedia or google for something like CIDR explanation.
Hope that helps :)
BTW Although your original question was on-topic it was asked in the answers, that's why it was deleted.