HOW to get back to original scale of model? Accidentally ignored "do you want to rescale?
Undo.
It’s not quite clear to me what you mean.
Did you apply the ‘Scale’ tool to (part of) your model?
Or did you apply the ‘Tape Measure’ tool to actually try to *resize (part of) your model.
If the first, there is a ‘Reset scale’ in the right click context menu for groups and for components, not for basic geometry.
If the latter, there is the option to *resize (*b.t.w. it is not rescale) your model again if you have a known length to then apply in the ‘Tape Measure’ tool operation once more on (same part of) your model.
Or use ‘Undo’ if still possible, as mentioned above by @endlessfix