oops, i only now understand you’ve unscrewed the slider tray without taking any measurements… My bad.
Somehow you should be able to get build platform in building position so it would push the slider tray in its position while maintaining access to the bolts the slider is screwed down with. Problem is, you probably need to short circuit the resin sensor as build platform will only come down if sensor is triggered. Also, when the resin tray is in its position, you can’t get to the screws. And maybe the build platform also covers the screws positions. Can’t check, as i don’ dare to take out my tray because my tray sensor is malfunctioning and i’m waiting for spare part to arrive before i’m willing to take it out.
Maybe you can sacrifice a tray & drill holes where the screws are so you can reach them with tray in place. Maybe you’ll have to sacrifice a build platform too and drill holes/cut parts away so you can reach screws through build platform too.
OK, maybe not the best ideas if you still have warranty, or are willing to pay formlabs to do the calibration for you. But should you think this is too costly (Euro 850 approx), and have an old tray & building platform to waste, that’s what i’ would try.
Hey, only my 2 cents, have not done this myself but just thinking along and suggesting what i would try if it would happen to me.