The repo is cloned to $HOME/.nextflow/assets/nf-core. I assume deleting the nf-core folder will fix this, but without a reproducible environtment of your situation it is hard to predict.
I’m sorry, you’re correct. $HOME/.nextflow/assets is for assets pulled by Nextflow (if you run nextflow run nf-core/rnaseq -profile test, docker --outdir results, for example, the pipeline will be pulled to $HOME/.nextflow/assets).
For assets managed by the nf-core tools, it’s $HOME/.config/nfcore.