How ro access docker volume files from the code on docker container

Question

i have creted a docker volume with such command

docker run -ti --rm -v TestVolume1:/testvolume1 ubuntu

then i created a file there, called TestFile.txt and added text to it

Also i have a simple "Hello world" .net core app with Dockerfile

FROM mcr.microsoft.com/dotnet/aspnet:6.0
COPY bin/Release/net6.0/publish/ ShareFileTestInstance1/
WORKDIR /ShareFileTestInstance1
ENTRYPOINT ["dotnet", "ShareFileTestInstance1.dll"]

I published it using

dotnet publish -c Release

then ran

docker build -t counter-image -f Dockerfile .

And finally executed

docker run -it --rm --name=counter-container counter-image -v TestVolume1:/testvolume1 ubuntu

to run my app with a docker volume

So what i want to achive to access a file which is in a volume("TestFile.txt" in my case) from a code in the container.

for example

Console.WriteLine(File.Exists("WHAT FILE PATH HAS TO BE HERE") ? "File exists." : "File does not exist.");

Is it also possible to combine all this stuff in a Dockerfile? I want to add one more container next and connect to the volume to save data there.