Yes, you can, as long as the old tattooing is significantly faded down enough. You can always send me a photo before coming in for a consultation to check.
Please be aware, however, that old tattooing cannot completely be concealed, so you will be able to see the residual tone of the faded tattoo underneath the Microblading.
Justine recommends a Combo Brow of Microblading and Shading or a Powder Brow to cover an old tattoo if it hasn’t faded enough for Microblading alone. There may also be an element of colour correction on old Permanent Makeup, so this may take up to 3 sessions.