I'm just starting to assemble the latest project using a Nano33BLE. Slightly disconcerted to find that the legends with logical pin numbering are on the opposite side of the board to the components, so if you solder the headers on in a way that allows you to see the legends the reset button is underneath and inaccessible! Not so clever when it comes to connecting up and troubleshooting...
Right. After connecting this board to a breadboard, it's difficult to figure out which pin is which number 
Print a pin reference diagram and place it next to your wiring, on your bench. You can perform a reset by grounding the reset pin.
It looks like there isn't much space for legends on the component side. I think that is the reason why it's on the back...
I use double length headers and plug mine in with the legends up. That way I can still use jumpers on the module pins. Like @anon57585045 says, the reset pin is right there next to ground. Easy to short with just about anything handy.
Thanks, I'll use a separate reset button then. Building this on strip board, some sticky labels to show which pin is which.
Unfortunately there are several of the newer boards that have the pin labeling on the back. The board was designed so that there are no components on the back side, to allow the board to be directly soldered down to a circuit board, which is the reason for the castellated pads along the edges.
Designing the board to allow it to be soldered to a PCB then putting the pin labels on the back is nonsensical.
Great once the circuit is tested and the PCB layout is finalised but until then very inconvenient
I still wouldn't solder it directly if it can take headers which it looks as though it does.
A photo or an index card of pins etc. is always useful especially where not so good eyesight is involved.