If you do not have (or don't want to use) the honey or sugar to raise your alcohol = acetic acid to the 5%. Apple skins and cores may not get this level. However you have options.
The boiling point of acetic acid is 244.6 °F while the boiling point of water is 212°F. If you have a still, you can boil vinegar / water mix to remove some of the water and increase and concentration of acetic acid content. This is not an zoetrope so as the distilling vapor rises from 212°F toward 244.6 °F you will begin to lose some of your acetic acid content.
Alternatively, you are freezing out acetic acid, which has a melting point of 62.6oF. You can freezer out and filter it to give you very concentrated acetic acid. Cool vinegar and keep the temperature below 60.8oF degrees and above 41oF and fish out acetic acid “ice” and re-dilute it to the % you want.