Customized SF Symbol

I need to create a custom symbol for use for Tabs in my SwiftUI app.
The only on-line references is a tutorial for the Affinity application.

However I notice Omnigraffle does open a SF Symbol.svg file.

I need a tutorial on how to edit/customize it.

Any references?

I would start here ( but may or may not answer your question.

If it is an SVG, you could create a stencil from the SVG. Create a new resource, import the SVG into a layer and save. Should be all you really need to do.

Going of the top of my head so may be missing some steps.

Your precise requirement is not clear. Could you please state it precisely.