50MHz to 1Hz

divide it by 50 000 000

Depending on what you want to do with it, it may be a better idea to do a clock enable rather than a new clock signal.

Use a counter. In your 50MHz clock domain; count to 25,000,000. Each time you reach 25,000,000 toggle your 1Hz clock and reset your counter:

module clk_1(
    input           clk_50mhz,
    input           reset_n,
    output  reg     clk_1hz
);
reg   count;
always @(posedge clk_50mhz or negedge reset_n)
    if(!reset_n) begin
                        count   <= 25'd2499999;
                        clk_1hz <= 1'b0;
    end else begin
                        count   <= count + 25'h1ffffff;
        if(!count) begin
                        count   <= 25'd2499999;
                        clk_1hz <= ~clk_1hz;
        end
    end
endmodule