Both bunnies will need their own space, this is really important so that the new bunny can feel comfortable. Do not attempt swapping toys/litter trays until the bunny has settled- ensure bunnies are both fixed before doing this step as it will only add to frustration if the bunny is unfixed smelling another- which can lead into territorial outbursts due to being so bewildered. As I mainly sell to indoor homes; here is a brief overview of recommendations...
If your bunny is in a pen, set up a side by side pen (ensuring it either has a roof or is very high) and zip tie some smaller mesh on the sides so that there can be no nipping, but they can smell one another.
If your bunny is free roam, you must ensure the new bunny has a safe space to call their own. They need a good size pen with a roof (I would always recommend a roof to prevent any jumping) - It is important the bunny has enough space to binky within the pen as this is their safe space until they're bonded - also allow them to alternate free roaming. Below you will find some options I would recommend for pens when keeping bunnies separate before bonding.
SET UP TOP TIPS: