Elite Rampa Zwift FTP

Hello to all.
I have purchased a used Elite Rampa and I am new to the Zwift world. I have found a six week plan which I am planning to follow in order to increase endurance in cycling. The plan is based on my FTP.

Although there is an Elite in-app way to calibrate my Rampa by using a power meter attached there is also another way to calibrate my turbo trainer by providing directly Power zones as values in the elite app.

Since I do not own a power meter is it safe to calculate my FTP using any of the available ftp tests provided by Zwift by using my non-calibrated trainer? Then I could provide the P zones in the app to calibrate it.

I know that the values provided by the Zwift ftp test are not going to be such accurate as per using a power meter but will they be close to the actual ?

Thank you in advance!