Can you some how get a gear on that front axle and make a small plate mount like this one only smaller.
https://rctruckandconstruction.com/s...ead.php?t=2037
Like you said it isn't fast so a large ratio would give you some torque...and since it's only crawling along you might not need bearings..... but I'm kind of new at this so...... I'm not even sure I would worry about making it "steer" just move forward and back....