Remove Kubernetes cluster setting from lens

I guess it depends on how have you installed it. I did with snap.

$ ps xaf | grep lens19987 tty2     Sl+    0:43              |   \_ /snap/kontena-lens/102/kontena-lens --no-sandbox20143 tty2     S+     0:00              |       \_ /snap/kontena-lens/102/kontena-lens --type=zygote --no-sandbox20173 tty2     Sl+    0:14              |       \_ /snap/kontena-lens/102/kontena-lens --type=gpu-process --field-trial-handle=9357832544711732318,17456889164076765037,131072 --disable-features=LayoutNG,SpareRendererForSitePerProcess --no-sandbox --gpu-pre AAgAAAAAAAAYAAAAAAACAAAAAAAAAAIAAAAAAAAAA== --service-request-channel-token=951158852848288651520200 tty2     Sl+    0:20              |       \_ /snap/kontena-lens/102/kontena-lens --type=renderer --no-sandbox --field-trial-handle=9357832544711732318,17456889164076765037,131072 --disable-features=LayoutNG,SpareRendererForSitePerProcess --lang=en-US --app-path=/snap/kontena-lens/102/resources/app.asar --node-integration --webview-tag --no-sandbox --no-zygote --background-color=#1e2124 --num-raster-threads=2 --enable-main-frame-before-activation --service-request-channel-token=2649628508984870433 --renderer-client-id=6 --no-v8-untrusted-code-mitigations --shared-files=v8_context_snapshot_dat 10120561 tty2     Sl+    0:00              |       \_ /home/suren/snap/kontena-lens/102/.config/Lens/binaries/kubectl/1.17.4/kubectl proxy -p 46571 --kubeconfig /tmp/4pqp6k4zamb-8bk89ka3wf5-kubeconfig --accept-hosts xx.xx.xx.xx20573 tty2     Sl+    0:12              |       \_ /snap/kontena-lens/102/kontena-lens --type=renderer --no-sandbox --field-trial-handle=9357832544711732318,17456889164076765037,131072 --disable-features=LayoutNG,SpareRendererForSitePerProcess --lang=en-US --app-path=/snap/kontena-lens/102/resources/app.asar --no-sandbox --no-zygote --background-color=#fff --guest-instance-id=4 --enable-blink-features --disable-blink-features --num-raster-threads=2 --enable-main-frame-before-activation --service-request-channel-token=15119202706114490733 --renderer-client-id=11 --no-v8-untrusted-code-mitigations --shared-files=v8_context_snapshot_dat 10120629 pts/0    Ss+    0:00              |       \_ /bin/bash --init-file /home/suren/snap/kontena-lens/102/.config/Lens/binaries/kubectl/1.15.11/.bash_set_path

So, in my case the config file is stored under /home/suren/snap/kontena-lens. Under /home/suren/snap/kontena-lens/WHATEVER/, there is a .config directory. I guess you will find what you need there.