What reles have you used? Arduino MKR 1000 is compatible with common reles?
I’m afraid to burn it, I burned my Genuino101 tested with a L392 for driver dc motor
Sainsmart makes some relay boards that work. Be sure to power the relay board from an external power source. Remove any jumper from the relay board if there is one. The In1- whatever will activate with 3.3v as long as you connect relay gnd to board gnd. The arduino 5v on board regulator cannot power the relays for long before poof!
You can use the 5 v relay, but you can use 3.3v also for alimentation of relay board. Connect the relay board GND and VCC to GND and 3.3vout Arduino mkr1000. After you can connect the output pin of arduino mkr1000 to in pin of relay.