scaling issue  

RE: scaling issue

I assume you are using Prusa Slicer!

find the size the model is going to print, in your current setup 

in my example I have used Gandalf the grey's staff

https://www.thingiverse.com/thing:2284353/files

find the size you actually want it to be   (Say 100mm)

when I load it into Prusa Slicer the model is 37.66 mm tall and has errors in it

click the error triangle as shown and windows (if you are using windows,) will attempt to repair the model using NetFab

in the right hand window, you have the model dimensions, 37.66mm
let's say I wanted the model to be 100mm tall instead

If you simply edit the Z Height to be 100mm, then Prusa Slicer will re scale the model, to make it 100mm tall
as shown above

prusa slicer will select the correct scaling factor, and enlarge as required

and then set the print settings, slice and print as required

regards Joan

Note, 
If the model is Multipart you may have to scale each part by the same amount to re-size it... 
but this may result in the model being too latge for the build volume
in which case
you would probably be best re assembling the parts into the whole staff, as a single STL, re scaling it, and then cutting the model into say 200mm tall pieces and printing it as several enlarged parts.