How do I move a project (an XPO file), (tables, forms) from Ax 2012 R3 to Dynamics 365?
As far as I know there is no way to convert an .xpo file into something that could be used in D365fO.
If you only want to move a few small objects, my suggestion would be to just reimplement them in D365fO.
Otherwise you should take a look at the Code Upgrade process, basically you want to move your objects to a new model, install that model on a clean AX 2012 R3 system, then upload the modelstore of that system to the LCS code upgrade service. More details in the following links: