Dahlias from seed -overwinter advice

[Whenitsjustyourclockreading505]

I had a stunning dahlia that sadly rotted earlier this year. As I I had harvested seeds off it last year I planted them late spring. I thought they had failed but, weeks & weeks later noticed one lone tiny plant growing. It is now just 2.5 inches tall. I know it isn’t going to flower this year but have hopes that next year it will flower and have developed a tuber for me to lift.
My question is how do I over winter it to get it through to next spring?
Will I have to bring the little pot in & stick it on a windowsill & water it all winter?
I can’t find any info on line about what to do with young dahlias over winter -I suppose because they aren’t generally it young & tiny still at this time of year!
TIA.

If your new dahlias have tubers, you will be able to overwinter them. Lift the tuber, store it and plant out in the spring.

If your seedlings don’t form a tuber, they won’t be able to overwinter. There’s still time for the tuber to form, it’s been a late season.

Leave it in the pot of soil. Put the pot somewhere frost free such as a greenhouse. It will grow next year.

I don’t think a tuber will have developed.
So, one for bringing in, one thinking it won’t survive. I will have hope because it was a stunner and I can’t seem to find one like it to buy.

I don’t have a greenhouse so it would have to be the kitchen windowsill.