I wonder why you need a legacy address.
If you are trying to withdraw from a service that doesn't support withdrawing to segwit addresses, take note that segwit soft fork was implemented more than 5 years ago and if a service doesn't support segwit addresses yet, it should be avoided.
If you used bitcoin core, on receive tab, select Amouth on Right box, then choose base 58 (legacy). because bitcoin core set segwit address by default so you have to manually do it change.
You don't need to enter the amount when generating a new address in bitcoin core. You just need to set the address type to "legacy" and click on "Create new receiving address".