The following link describes the use of LiftPulse and iSeismometer. Liftpulse is no longer available on iOS as you have discovered and was dropped after the company was purchased by Google. iSeismometer is a less user friendly app but one of.. if not the earliest apps to be used for human tremor testing after originally being developed to record earthquakes!
StudyMyTremor should be a good alternative to the above apps. Even though StudyMyTremor has a fixed 1 minute sampling time, it will show ( in the details page) the predominant peak. So if you can only stand for a short period and you sit for the remainder of the time the detail page should give you a useful chart. Screen captures would be a good method of conveniently and quickly saving the charts. The technique described in the following research should be helpful:
https://onlinelibrary.wiley.com/doi/pdf ... mdc3.12547
The phone was placed just above patella on the quadri-ceps tendon while sitting and it was held in place with a tourniquet. Recording started after the participants stood up(Fig. 1). App1 displays frequency power spectrum with a visible peak on the graph along with a software detected peak frequency as a number (Fig. 2). In App1 we recorded both the “predominant peak” (provided by the app), and any visible second peak (see results). If any of those two measures showed a tremor within the OT range, this was counted as a positive test.