Hello Ishan, sorry for my late response. I doublechecked this. When you use a record-changed before-save flow you cannot use an action. Action element disappears from the left-panel. Therefore you will not be able to use the submit for approval action.
BRDPro Consulting 
How to use core actions like submit for approval in this type of flow?
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Hello Ishan, sorry for my late response. I doublechecked this. When you use a record-changed before-save flow you cannot use an action. Action element disappears from the left-panel. Therefore you will not be able to use the submit for approval action.
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