Hi Devadarsi, Vinay is absolutely correct. The Standard save button is out of the box functionality. Any custom save button has been created to override the standard functionality. You can generally override the new, view, edit, and tab buttons with a lightning component (discussed here https://www.forcetalks.com/blog/how-to-override-standard-buttons-with-lightning-component/ and an alternative Aura component is demonstrated with walk-through instructions here https://trailhead.salesforce.com/en/content/learn/projects/workshop-override-standard-action/override_4 .)
The Standard save button is salesforce inbuild functionality and you cannot make a change.
The custom save button is implemented by Developer using VF page.
Thanks,
Vinay Kumar