I have configured the public v1 string in the dude under settings, server configuration, snmp

Now I need to setup the string in my mk devices. I am running ros 4.6. I see under IP the snmp option but it seems to be for setting up an snmp server?

Where can I change the snmp string in my mk router boards with the winbox gui so that snmp will work?

You are in the right spot. Edit the "public" profile you say and change the name to the desired snmp string. Be sure to go to SNMP settings and enable SNMP as well.