50% open of previous candle

Before solving this we need to know what you mean b:

"open at least 50% of the previous candle"

I suspect what you meant to say was:

The open of the current candle is above or below the middle of the previous bar's high to low range. But we need to know which, is it above the mid point or below the mid point?

I will update the title of your question once you explain these missing details.

Either way, the scan is very easy to create using the Condition Wizard:

https://www.hahn-tech.com/thinkorswim-condition-wizard/

Screenshot below shows how to set this up. But you will want to look at the study settings and adjust it as needed. In this example I have provided, the open must be greater than the mid point of the previous bar and the 20 SMA is crossing above the 50 SMA within the last two bars.