if you want to just change the ‘look’ of the H2 heading using on the blog / archives then you can style it separately in Customizer > Typography > Headings –> Archive Content Title (H2)
If you need to change the HTML Element tags from <H2> to <H3> then Leo explains here:
The option would beline height which can be set in customizer > typography.
If you have more questions regarding this, can you please open a new topic and link us to your site?