To convert ost to pst in Outlook 2019, I sincerely suggest you go for SysInspire ost to pst converter.
Steps to convert ost to pst by using SysInspire Converter for ost to pst conversion.
install, install and install the SysInspire ost to pst Converter software.
Click ‘Browse’ to select the ost file or use the ‘Find’ option to search and select ost fille
get a sneak peek at the mailbox items after the scanning of the ost files.
Under the ‘Home’ tab, Click on the ‘Save Converted File as pst' button
to save the file in pst format after conversion.
Select the ‘pst’ option and click ‘Browse’ to choose a save location
Click ‘OK’ to begin exporting mailbox items from the ost file to pst in Outlook 2019.
Advanced features like pst split, date filter, other saving configurations etc., are
available which will surely induce the operators to use this automated appliance.
More info:- Convert OST file to PST