my friend's number which is registered to apple id was lost and he has forgotten his apple id password. Can I help him using my own apple id and password?

You cannot help him with your account information , but you can provide this information to your friend.

This Apple article has instructions for what to do if you have forgotten your Apple account password —> If you forgot your Apple ID password - Apple Support

or go directly to this link —> http://iforgot.apple.com/

If you didn't receive your verification or reset email, read this Apple Support article: If you didn't receive your verification or reset email - Apple Support

"When you make certain updates to your Apple ID, we’ll send you an email to help you complete the update. For example, you might have reset your password, reset your security questions, or added a new email address to your account."

If you find you can’t sign in, reset your password, or receive verification codes, you can request account recovery (read this support article: How to use account recovery when you can’t reset your Apple ID password - Apple Support ) to regain access to your account. Account recovery might take a few days or longer, depending on the specific account information you can provide to verify your identity.

If you still need help this page provides country-specific Apple Support contact information for customers seeking help ➞ Contact Apple for support and service - Apple Support

An Appel ID can be recovered:

If you forgot your Apple ID email address or phone number - Apple Support

And the Apple ID password can be reset:

If you forgot your Apple ID password - Apple Support

In case this does not work, you'll have to use the Account Recovery:

How to use account recovery when you can’t reset your Apple ID password - Apple Support