Put inside, pay less income tax and can withdraw back your money at 55 years old. You don't want?

A lot of people see it as a place to pay less tax and just pick any fund. However why should you just think of tax relief and choose not to "grow it"? You can have both
tax relief + growing your money 

i think prs return is not bad plus the tax reduction. however need to balanve with liquidity management.

Just put max RM3k/year until 2021. If tax relief is not continues, stop topping up loh.

Er buy RM3000 worth (can be lump sum or in small amount) of PRS from FSM (0% service charge) or agent/banks (3% service charge). After buying keep the receipt. Fill up your income tax. There's a section there with Private Retirement Scheme (PRS), fill up RM3000 to get your tax relief. Keep your PRS receipt for record purpose.

RM3000/year tax relief is valid until 2021 unless it's continue by the govt.

2 years back means forgo it. You cannot claim it back as the tax year have pass. You have to manually fill up that column when you are filing for income tax.

When you buy from the fund house (eg. Cimb P, Affin hwang, Public Mutual, etc), they will send you a statement by post on how much you have. Keep that as record.

Manually fill up means do your tax filling online. If you do income tax filling, you should be able to see it.