Need to merge yield data for each GDMID with shape file and plot the map filled with yield

Question

I am trying to plot an Indian district shapefile filled with modeled yield, corresponding to each GDMID, common in shapefile and .rds dataframe. I need to first merge the Yield data with respect to each GDMID from the .RDS file with the district shapefile of India. Each district is represented by a GDMID. After merging, the Indian district map filled with modeled yield values needs to be plotted. Shape file has five features, and one of them is "GDMID".

I feel there is something wrong with my code for merging and plotting by ggplot.

I have provided my files in the given link. link of code, shape file and .RDS data frame

I am new to the spatial mapping with R so needs help clarity with steps.

Thanks in advance, Ranjeet