hello i have Iphone 5c but the previous oner foget her apple ID and the password so i cannot start the phone please i need help

Forgot their Apple ID and/or password.

1. If the previous owner does not remember the Apple ID Password then ask them to follow the steps given in this Apple Article -> If you forgot your Apple ID password - Apple Support
2. If the previous owner does not remember the Apple ID then ask them to follow the steps given in this Apple Article -> If you forgot your Apple ID - Apple Support

If you are the owner or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the owner and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password with you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their Apple ID.