For instance - what would be the PCF for RSI at a five week low?

If it is a 14-period plain RSI without Wilder's smoothing and and you are using a Daily time frame, a Condition Formula for this could be written as (estimating 5-weeks as 25-daily bars):

RSI14 = MIN(RSI14,25)

PCF Formula Descriptions
Handy PCF example formulas to help you learn the syntax of PCFs!

A similar formula for a 14-period RSI- Wilder's indicator with Wilder's smoothing would be way too long and slow to be practical or post in the forums. That said, we can create the Condition from the chart.

Add the RSI - Wilder's indicator to the chart and then add 24-Period Donchian Channels to the RSI - Wilder's indicator.

Adding and Moving Indicators

Then click on the RSI - Wilder's indicator and select Create Scan Condition. You will want to create a condition for the RSI to be crossing down through the lower Donchian Channel.

Create Conditions from Your Chart

Another option would be to skip the Donchian Channels and just click on the RSI and select Create Scan Condition. You could choose New Low from the list and set the period as desired.