"I understand your concern" is correct and usable in written English. You can use it when someone expresses concern or worry, and you want to show that you understand and sympathize with them. For example, you could say, "I understand your concern about not having a backup plan for the project. Let's come up with some ideas together.".
I understand your concern.
"But I understand your concern, and I appreciate it.
I understand your concern about butting into your employee's personal business.
I understand your concern, but telling them not to do it isn't going to work.
JON LEE ANDERSON: I understand your concerns and they are valid given Haiti's past.
I understand your concerns about the ethics involved in interviewing Alzheimer's patients.
In a message to the NRA, Graham added: "I understand your concerns, but every right has boundaries on it".
Since I tried Ludwig back in 2017, I have been constantly using it in both editing and translation. Ever since, I suggest it to my translators at ProSciEditing.
Justyna Jupowicz-Kozak
CEO of Professional Science Editing for Scientists @ prosciediting.com