Solving Delayed differential equation symbolically

Here I want to solve a delayed differential equation by symbolic manupulation

y is function of t and td is the delay in the signal ie

diff(y)=a*y(t-td)

how do I solve this equation

[Walter Roberson]

https://www.mathworks.com/help/symbolic/examples/pade-approximant-of-time-delay-input.html might help, perhaps.