Draining and refilling a cooling system is not hard to DIY, but you must be responsible with the coolant - it’s poisonous to anything that drinks any.
I would drain the radiator (and block, if it has its own drain with the heater set to Hot. It doesn’t have to be running, but the Hot setting is needed on many vehicles to open the coolant circuit to and from the heater core. Then refill with plain water (maybe with a cooling system cleaner, too) and run it for some minutes or hours. Repeat the drain and refill a time or two, using fresh water especially if you’ve used a chemical. When it’s clean water coming out, then put in the correct amount of antifreeze.
This is all described in many DIY books, but the above will get you started.
Of course, after a while you’ll be checking to see if that foamy stuff is back.
Some antifreezes react like that to air. Maybe your coolant recovery tank’s hose to the radiator filler neck, or the rad cap, is letting air in.