Use a 3/8 inch box end wrench. No heat needed. Just need the right tool.
Every pinball toolbox should have an assortment of small combination wrenches (boxed end and open end) in their toolbox. $22 at Harbor Freight.
https://www.harborfreight.com/fully-polished-sae-metric-combination-wrench-set-32-piece-68854.html