In the Design view, drop a Panel in the position you want to place the tiledlayout.
You will have to create in code. Click code view. Click on AppInputArguments, type in varargin. It will create a startup function.
Click on Property and add a property called tiledlayout. (If you want to access it from workspace, make it public)
Inside the function you can create a tiledlayout, and initialise anything else.
If your gridlayout was only for the axes, you can replace it with a panel as above. If your gridlayout also contains other uielements, you will need to keep it. just place a panel in the gridlayout in the position where you want to put the tiledlayout.
During creation of the tiledlayout you can specify how many tiles you want.
When you are plotting use the nexttile function to get the axes to plot on.
function startupFcn(app, varargin)
m = 2;
n = 4;
app.tiledlayout = tiledlayout(app.Panel,m,n);
tilenum = 1;
ax = nexttile(app.tiledlayout,tilenum);