sorry to hear about your tadpole/froglet. Unfortunately I've had this happened several times before, but I have found success, which I will share with you. :-)
I should mention this depends on how many you have. The first set of instructions are for a lot, a few hundred.
Almost every year the local frogs lay eggs too late in the season and in the fall I'm breaking through the ice to remove tadpoles from my above ground pool, which freezes solid through the winter.
Once I manage to collect as many as I cant find...
I usually keep the tadpoles in a storage bin, with clean unchlorinated water, a few cups or small containers they can hide in, a few aquatic plants & feed them fishflakes, until they get their back legs.
When the back legs look more like frog legs, bent, I move only those tads into another container that I put several large rocks or gravel in, on a sloping angle like a shore line, that they can climb up. It should definately allow their heads to be above the water line or even out of the water, at the top of the slope. You can have a platform at the top where they can sit out of the water completely, many of mine do this at this stage so dont be alarmed.
Once they sprout one or both of their front legs I then put them in another container with mostly gravel with a very shallow pool/pond area, about an inch or enough water they could stand in but reach the surface, about 2/3's pond,1/3 gravel land. I put some moss around the waters edge and put several plant clipping in there too.
Attachment 53853
If you only have one or a few you can do the gravel set up with a larger, deeper pond/pool area, with less "land" area and simply ajust the water depth & land/pool area as the tadpoles morph.
Best of luck, hope this helps :-)