Due to restriction on access for corporate git repository, I want to provide the source code as input (tar or zip file) to tekton. Can anyone guide me on how to achieve it.
The details are going to depend on how you are providing the tar/zip to your pipeline.
But the gist is to remember that Pipeline tasks are really just containers. (Except with a bit of magic around things like arguments, sequencing, UI etc.) So asking "how do I provide source code" is essentially the same question as "how would I do this if I were doing this in a script inside a container".
If you already have the tar/zip in a PVC, then you can just mount two workspaces (one with your input tar/zip, and one where you are outputting your source files) and execute the tar (or zip) command from the one mount point to the other. (Just make sure to use a base image that has tar in it.)
If you don't already have the tar/zip, you might need to use scp or something like that first, but all of the principles look the same. Take a look at the YAML for the out of the box Tasks and you will see that they are actually quite simple under the covers.