how to remove the usage of bootstrap ? And rely on material UI instead .
Instead of importing Bootstrap and using it’s classes, import Material UI.
Is this same for a large code base too ?
Yes. The larger the code base is, the more time it takes removing all the dependencies on Bootstrap, but it’s the same thing.
Is there any technique which is less time consuming on a large code base ?
You could try writing a script to make a first pass at removing Bootstrap references, but since Material is it’s own design paradigm, an actual human is going to have to go through all of the affected views and make sure they work and look right.