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@dr_nosh
The diameter of the frame cups should be marked on them. Once you know this then you have to measure the inside diameter of the head tube. The cups need to be a few thou (inches) smaller. Reaming is a metal removal process to remove very small amounts of material to just size, or even 'round' the headtube.
The cups must be pressed in 'square'.
The crown bearing is also a press fit.
The stack height of the bearing set must also be considered to ensure that the steerer tube is long enough to ensure sufficient engagement of the threaded top bearing and lock nut.
Do not force the bearing cups into the headtube - you will stretch the tube.
Conclusion = Go to the LBS or another with knowledge, tools, experience.