Units in slot 3 and 4 in the party are the ones in front of the Golem, while slot 1 and 2 are the ones next to it. Doing the raid in auto mode may make your units closer to the minions to attack them instead of Golem. You might get better success if you put your main damage dealers in slot 3 and 4 instead.
Golem is weak to both magic and Wind element, so Howlet and Little Leela (Halloween) works best for the fight since they take advantage of both.
Garvall is also the main recommended choice since he's one of the "bonus" units, and a very hard hitting mage.
Golem barely has any elemental resistances, so you still have plenty of options because most strong mages can work. Having Adelard can help make other mages more viable since he has Imperil .
Rhaldor is the main ideal choice since he's a Fire Striker with the highest raid bonus, while Oelde is a fairly old unit that most people may have access to.
If you are using units that uses Strike attacks as their sub job, you might need to disable their main job's skills to make sure they use mainly Strike attacks in auto battle.
The next best choices are strong magic attackers despite its 5% magic resistance as long as it's not Wind magic, so Howlet and Little Leela (halloween) won't be as effective.
Garvall, Sakura, Kilphe, and Ildyra are easy recommendations, especially if you already have them fully built.
Golem Stats & Resistances
Max Level Stats
Accuracy Up, HP Debuff Res+999%, AGI Debuff Res+999%.