Where can I find my tax liability for 2019 if I filled online with h&r

You'll need to get a copy of your 2019 return from H&R Block.  You may also be able to find the amount by accessing your 2019 transcript (abbreviated version) of your return.  Use the link below to access your transcript on the IRS webpage.

Get Transcript | Internal Revenue Service (irs.gov)

2019 form 1040 line 16...