How do i replace a lost credit card?

Look at a recent credit card statement. There's a phone number on there to call and report the lost card.

If it's a Costco credit card, citi is the bank that issues the card. I would contact citi about it.

I would suggest you contact your credit card company. If it is one of their credit cards, I would think that you would still go to the card company.

Go to you nearest Costco