Pre delivery expenses Medisave

Hi! 1st time mum here and very confused on Medisave. I have been paying upfront for pre delivery expenses and Medisave says you can claim up to $900 for this. I am not sure what claiming means? If I already paid 900$upfront and the bills can only be submitted at delivery, I’m confused where the reimbursement goes - do I get it to my bank account? Or where does the 900$ go, thank you! Sorry if silly question but I’m really really confused. Thanks!