According to the IRS:
“If you and your spouse made separate estimated tax payments for 2018 and you file separate returns, you can take credit only for your own payments.
If you made joint estimated tax payments, you must decide how to divide the payments between your returns. One of you can claim all of the estimated tax paid and the other none, or you can divide it in any other way you agree on. If you cannot agree, you must divide the payments in proportion to each spouse's individual tax as shown on your separate returns for 2018.”