how to run gpu on this miner? it wont detect gtx 1050ti. how to enable mining with gpu?

I just disabled crossfire and both GPU are now mining.

I have had my Crossfire GPU even before the mining craze. Would be nice to use them both. Works for both GPU on other miners would be nice to have it work here. More convenient than having to convert altcoins.

So how many GPUs this app can utilise?

so, the used with more than one GPUs mining is possible or not?

Good point on multiple or buggy GPUs - a lot of times GPU manufacturers optimize for gaming performance over compute stability and often break things between releases.

We are working on an update which should handle buggy/crashing drivers a bit better in the future (i.e. automatically stop using those GPUs).

On my case, I have a notebook with two gpus the first is the intel hd4000 and the second the AMD hd8870m.
First, I see only the processor is used (running at 35kH/s), after some time, the amd gpu start running (then the score goes to 60-70kH/s), and finally, when the intel gpu starts, the end score can reach 80kH/s...
but many times, the intel gpu just stops running, and only left the cpu + amd gpu for the software to use

or ability to map which gpu to use

This should already be happening - some things to double check:

Bitcoin Miner defaults to efficiency mode where it will try to minimize power consumption vs yield. If you run in performance mode you should see higher hash rates at the expense of heat and power consumption.

Make sure AMD Crossfire or NVidia SLI are disabled when mining. Both cause the operating system to report multiple GPUs as one to apps, and both Crossfire and SLI are designed for graphics rendering (they have no logic to divide up compute workloads). On our development systems Cossfire/SLI cause only the first GPU to be used for mining! Unfortunately, Microsoft blocks access to the programming interfaces needed to automatically adjust this setting in Windows Store apps so this has to be done manually.

If running in a VM, make sure the VM can do passthrough of the GPU (some VMs mess with the GPU compute bytecode which affects performance).

We're also working on improving the settings UI in the future to list all of the devices Bitcoin Miner is using (or not).