Use of Landsat_5 and landsat_8 NDVI 8 day repetition cycle in the land productivity indicator

[maptomeaning-muluk]

Hello,
I am Akshay, pursuing master's degree in Geoinformatics. As a part of it I am using this plugin for assessment of land Degradation. My objecive is to modify this plugin so that it can directly fetch the landsat 5 and landsat 8 NDVI products for calculating the land productivity.
But I am unable to locate from where it is importing the data sets can anybody please help me in that.

Also, if thats not possible how can I use the actual land productivity algorithm in jupyter notebook or pycharm for getting the output