As a text record you copy a part of the contents from the file
/etc/opendkim/keys/yourdomain.com/mail.txt (or
default.txt), it data should start from
v=DKIM1; k=rsa; to the end, without the quotes as you can see it’s in quotes.
It'll look like this example:
Code:
v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPzE0GmvFwAQsgcFzopy4zMNWUbL6JM5XIyjBy3bUnANI5axeb/Lw/GBjUoSFLEiO80Tt8m3A5YrBKcodRQQURYiW6/YtElhLupHyfcxQhfNLU4z9JUOJKPjcpMZCj0Xv873QgVOl+7U605JdBHSPOx4ybBZwDq68cw9YFYRPmEwIDAQAB
You'll copy this code as a txt record to your DNS host.