"What do you mean by this"

Not needing to pay a large amount at the time of filing doesn't affect how much they owed in taxes. You are supposed to be able to explain that. Your title asked to "reduce tax liability" and that isn't your issue really, because you asked, "Client does not want to owe again this year like last year."

When your financial life results in, "I owe taxes" meaning, you have taxable income or gain, you are supposed to have prepaid some of it. That is why there is W2 withholding, Social Security withholding, required withholding on Trad IRA and retirement distributions, and that is why there is a provision for making estimate payments. These are not Taxes. They are Prepayments.

This is why uninformed people love getting a refund. They think they are getting a return of taxes. Most times (setting aside the topic of refundable credits), they are getting their own money returned to them, because they overpaid the prepayment.

The opposite is true. Paying or not paying a balance is not what they are paying in taxes; it's paying the rest of the taxes they owe. They already paid some, in most cases, so that payment is not, "I paid $X in taxes when I filed" as if that is the amount of taxes they owed. It's only the balance they owed. This is what you asked, how to not have to pay at the end.

When they ask you to help them not pay, we are not trying not to pay taxes (beyond the regulation's provisions); we are trying not to owe more at the time of filing.

By prepayment through withholding and/or estimates, they simply are paying their liability over time, instead of only at the point of filing the tax return. But, again, uninformed people do not see it that way.

If this was my client, I would ask them if they mind being responsible for scheduling or for paying manually, on a quarterly cycle, based on some planning we will do together. If they answer "let's do this," then we would look at known income streams, safe harbor, and discuss that any unexpected windfall or activity might require an additional amount be paid at the time it happens and we don't even need withholding. If they do not want to be actively involved, we set up withholding everywhere possible and/or can schedule some estimates and our target can be based on safe harbor, and that can be a bit of a yoyo, but that's what they want.