Below I have taken the 13 team schedule generated by my Excel file. Then in the final column I have written down the team who currently has a bye.
(B M) (C L) (D K) (E J) (F I) (G H) A
(C A) (D M) (E L) (F K) (G J) (H I) B
(D B) (E A) (F M) (G L) (H K) (I J) C
(E C) (F B) (G A) (H M) (I L) (J K) D
(F D) (G C) (H B) (I A) (J M) (K L) E
(G E) (H D) (I C) (J B) (K A) (L M) F
(H F) (I E) (J D) (K C) (L B) (M A) G
(I G) (J F) (K E) (L D) (M C) (A B) H
(J H) (K G) (L F) (M E) (A D) (B C) I
(K I) (L H) (M G) (A F) (B E) (C D) J
(L J) (M I) (A H) (B G) (C F) (D E) K
(M K) (A J) (B I) (C H) (D G) (E F) L
(A L) (B K) (C J) (D I) (E H) (F G) M
Now rearrange the order of the rounds so that the last column of byes corresponds exactly to the teams playing in the last round above.
(B M) (C L) (D K) (E J) (F I) (G H) A
(M K) (A J) (B I) (C H) (D G) (E F) L
(C A) (D M) (E L) (F K) (G J) (H I) B
(L J) (M I) (A H) (B G) (C F) (D E) K
(D B) (E A) (F M) (G L) (H K) (I J) C
(K I) (L H) (M G) (A F) (B E) (C D) J
(E C) (F B) (G A) (H M) (I L) (J K) D
(J H) (K G) (L F) (M E) (A D) (B C) I
(F D) (G C) (H B) (I A) (J M) (K L) E
(I G) (J F) (K E) (L D) (M C) (A B) H
(G E) (H D) (I C) (J B) (K A) (L M) F
(H F) (I E) (J D) (K C) (L B) (M A) G
Finally pair off the rounds to form the weeks of your schedule adding the two byes from above as the extra match.
Week 1: BM CL DK EJ FI GH MK AJ BI CH DG EF AL
Week 2: CA DM EL FK GJ HI LJ MI AH BG CF DE BK
Week 3: DB EA FM GL HK IJ KI LH MG AF BE CD CJ
Week 4: EC FB GA HM IL JK JH KG LF ME AD BC DI
Week 5: FD GC HB IA JM KL IG JF KE LD MC AB EH
Week 6: GE HD IC JB KA LM HF IE JD KC LB MA FG
Ian.