To get a logic level from an open collector, just connect a pullup resistor of, say 10K ohms. As long as the resistor supplies the required current to your circuit, you're good to go.
Double check the current requirement at the input of your relay board and make sure the 10K resistor will supply enough current R = V/I, R is your pullup I is the input current, and V is the low limit for a logic high. You may find you have to lower the value of your pullup.