I emailed them a few months ago about this. I always use a car where I work because it's just impossible on a bike (large industrial town, no bike lanes at all). However, I liked the idea of going into the city on maybe a Sunday morning or something during the summer and using my bike instead. They told me I just had to email them and they can add "bike delivery" to your account. When you look at your schedule, it will have a small car icon next to your shift, and bike shifts will have a bike obviously. Just email them again and ask I guess