I am assuming that you are generating HDL code from a simulink model. I attached an example model for reference. Below is the procedure for replacing the default file header with a custom file header:
Right click on the subsystem you can go to Hdl Code>> Hdl Coder properties
Search for Customfileheadercomment. In the Custom file header comment, Enter the following comments
// Title : <%Title%>
// Project : <%Project%>
// Author : <%Author%>
// Hello : <%Hello%>
// Revision : $Revision$
// Date Modified : $Date$
Now generate HDL code for the subsystem. Open the generated HDL code(Subsystem.vhd) you can find the header section at the top. Whatever you specify in the Customfileheadercomment section will be present here
Current date and Author name won't be updated automatically. Whatever is set as Date and Author name, will be reflected in the generated code