I have an 01 Buick LeSabre that turns strong but will not start. I changed fuel pump and all. Could it be the relay switch? And we're is it?

The proper way to find the problem would be to pull a plug wire an see if it has spark or hook up a fuel pressure gauge an see if it has fuel pressure . Don't guess an just replace parts if you don't know how to test correctly .
https://www.youtube.com/watch?v=EB-hVxk4yus

Your vehicle doesn't have a reset switch . First off you would need to find out what's missing . You think a fuel reset problem . Knowing how these thing's work , training is how to find the problem . Could be a no spark problem . It take's special tools to test properly . Fuel pump pressure gauge , spark tester , scan tool . An you need factory service repair info. for checking
specifications . We don't guess as to what the problem is , we test . 048 Engine Hard to Start or No Start Scan Data for Starting Problems
GM Fuel Pump Relay Testing

Does it have spark ,is there fuel , is there compression ? If you have to ask you should take it to a qualified repair shop !

Change the fuel relay
Check this link
https://www.justanswer.com/buick/4bnwv-buick-lesabre-custom-fuel-pump-relay-located.html

Go to Autozone.com and register your vehicle for free to get the info you requested. Both fusebox details and wiring diagrams are available.

The 97 Lesabre doesn't have a fuel cut off switch like some other vehicles do. The test I use is to check for power at the fuel pump harness connector near the fuel tank. When you turn the key from Off to Run the computer will close the fuel pump relay and supply power to the pump for about two seconds then it will turn the relay back off until you actually are cranking the engine over. This is a two person test as you need someone to turn the key to "Run" as the other person is checking for power at the connector. If you have over about 120,000 miles then the odds are pretty good that the pump has failed but It's always best to verify it with a test. Good luck and hope this helps!

For 1999 Buick LeSabre - but you took #1 off the list, so here's the whole "failure to start" list:

Priority Action Part Type Cause
1 Inspect Battery Battery Discharged or Faulty.
2 Inspect Battery Cable Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Distributor Cap Distributor Cap Cracked or Burned.
3 Inspect Fuel Filter Clogged or Dirty Fuel Filter.
5 Inspect Ignition Coil Faulty Ignition Coil.
6 Inspect Wireset Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter Starter Motor Faulty.
9 Inspect Fuel Pump Low Fuel Pressure.
10 Inspect Starter Relay Faulty Starter Starter Relay
11 Inspect Fuel Pump Relay Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Motor Faulty Starter Motor
15 Inspect Fuel Injector Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer Clogged or Dirty Fuel Pump Strainer
17 Inspect Engine Control Computer Incorrect Operating Information Being Delivered and Sent From The EEC.
18 Inspect Fuel Tank Fuel Tank Empty.
19 Inspect Carburetor Carburetor Flooded or Faulty Choke.
20 Inspect Distributor Rotor Distributor Rotor broken, burned contacts, or loose
21 Inspect Distributor Worn, Loose, or Incorrectly Installed Distributor.

There is no cut off switch. Check all fuses and the fuel pump relay.

There is no fuel pump cut off switch on the LeSabre. Check the fuse and relay on the passenger side behind the glove box. There should be 4 black relays. The fuse pump is below this and the pump fuse is number 6. The other thing to keep in mind is the Pass lock system may not be recognizing the ignition key and has disabled the fuel pump from the ECM. Lets start with the fuse and relay first and we'll work on the Pass lock relearn process which takes about 30 min to do. Good luck and keep me posted, be glad to help.

Your vehicle's fuel pump relay is located on the relay center, behind the glove box, 2nd column of relays, 2nd one from the top.