The answer to your question is that it is not a great idea to do this, but you will find various answers to this question.
The bandwidth, and more importantly, latency between the GPU and RAM over the PCIe bus is an order of magnitude worse than between the GPU and VRAM, so if you are going to do that you might as well be number crunching on the CPU.
You can read the full article here.
When you optimise using cTrader do not select all the available parameters, instead, do sections at a time, an example would be to find the best settings for a single indicator and once you have these, fix these values and then move onto the next indicator or parameter.
This may also help you. https://clickalgo.com/cbot-optimization